Picture this: You are standing at the edge of a lagoon on a South Pacific island. The nearest village is 20 miles away, reachable only by boat. The water is as clear as air. Overhead, white fairy terns hover and peep among the coconut trees. Perhaps 100 yards away, you see a man strolling in the shallows. He is bald, bearded, and buck naked. He stoops every once in a while to pick up a shell or examine something in the sand.

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A lot of people wonder what happened to J. Craig Venter, the maverick biologist who a few years ago raced the US government to sequence the human genetic code. Well, you've found him. His pate is sunburned, and the beard is new since he graced the covers of Time and BusinessWeek. It makes him look younger and more relaxed - not that I ever saw him looking very tense, even when the genome race got ugly and his enemies were closing in. This afternoon, the only adversary he has to contend with is the occasional no-see-um nipping at some tender body part. "Nobody out here has ever heard of the human genome," he told me a week ago, when I first joined him in French Polynesia. "It's great."

Venter is here not just to enjoy himself, though he has been doing plenty of that. What separates him from your average 58-year-old nude beachcomber is that he's in the midst of a scientific enterprise as ambitious as anything he's ever done. Leaving colleagues and rivals to comb through the finished human code in search of individual genes, he has decided to sequence the genome of Mother Earth.

What we think of as life on this planet is only the surface layer of a vast undiscovered world. The great majority of Earth's species are bacteria and other microorganisms. They form the bottom of the food chain and orchestrate the cycling of carbon, nitrogen, and other nutrients through the ecosystem. They are the dark matter of life. They may also hold the key to generating a near-infinite amount of energy, developing powerful pharmaceuticals, and cleaning up the ecological messes our species has made. But we don't really know what they can do, because we don't even know what they are.

Venter wants to change that. He's circling the globe in his luxury yacht the Sorcerer II on an expedition that updates the great scientific voyages of the 18th and 19th centuries, notably Charles Darwin's journey aboard HMS Beagle. But instead of bagging his finds in bottles and gunnysacks, Venter is capturing their DNA on filter paper and shipping it to be sequenced and analyzed at his headquarters in Rockville, Maryland. The hope is to uncover tens or even hundreds of millions of new genes, an immense bolus of information on Earth's biodiversity. In the process, he's having a hell of a good time and getting a very good tan. "We're talking about an unknown world of enormous importance," says Harvard biologist and writer E. O. Wilson, who serves on the scientific advisory board of the Sorcerer II expedition. "Venter is one of the first to get serious about exploring that world in its totality. This is a guy who thinks big and acts accordingly."

He certainly talks big. "We will be able to extrapolate about all life from this survey," Venter says. "This will put everything Darwin missed into context."

For now, though, the expedition has run aground, snagged on an unanticipated political reef here in French-controlled waters. But it may all work out tomorrow. Right now, the sun is just beginning to soften toward sunset, and a gentle breeze is rustling the palms. Venter has disappeared in the direction of the boat, and one of his crew members, wearing a Sorcerer II T-shirt over her bathing suit, is waving me back. Must be close to dinnertime.

The last time I spent a few days with Venter on his yacht was in 2002 on St. Barts. He was in a much darker mood. He had just been fired as head of Celera Genomics and was hiding out in the Caribbean, licking his wounds. He had started the company four years before to prove that a technique called whole-genome shotgun sequencing could determine the identity and order of all DNA code in a human cell and do it much faster than the conventional method favored by the government-funded Human Genome Project. He had already made science history by using his technique to uncover the first genome of a bacterium, but most people doubted it would work on something as large and complicated as a human being. Undaunted, he pushed ahead, informing the leaders of the government program that they should just leave the human genome to him and sequence the mouse instead.

Venter also promised that he would give away the basic human code for free. Celera would make money by selling access to gobs of additional genomic information and the powerful bioinformatics software tools needed to interpret it. His critics claimed that he was trying to have it both ways, taking credit for providing the world with the code to human life and reaping profits for his shareholders at the same time. Venter cheerfully agreed.

Things didn't quite go according to plan. His gambit did indeed accelerate the pace of human DNA sequencing, and the shotgun approach has now become the standard method of decoding genomes. But galled by the effrontery of Venter's challenge, the Human Genome Project scientists closed ranks and ramped up their efforts quickly enough to offer a draft of the genome almost as fast as Celera's nine-month sprint. In June 2000, the increasingly bitter race came to an end in a politically manufactured tie celebrated at the White House. The détente with the public-program scientists lasted about as long as it takes to pack up a camera crew. And by that summer, Celera, once king of the startup biotech sector, had already begun a long sad slide into the stock-price cellar and corporate obscurity. "My greatest success is that I managed to get hated by both worlds," Venter told me on St. Barts.